Erroneous "auto can only be used for template function parameters"?

[Yuxuan Shui via Digitalmars-d-learn]

On Monday, 22 June 2015 at 13:49:21 UTC, Steven Schveighoffer 
wrote:
> On 6/20/15 10:26 PM, Yuxuan Shui wrote:
>> On Sunday, 21 June 2015 at 01:26:51 UTC, Adam D. Ruppe wrote:
>>> On Saturday, 20 June 2015 at 01:50:11 UTC, Yuxuan Shui wrote:
>>>> auto ref R) is indeed a template function, so I don't 
>>>> understand.
>>>
>>> But R is not a parameter on the function itself. It comes 
>>> from the
>>> outside template.
>>>
>>> Move it to the inside template, rewrite it as:
>>>
>>>     auto a(S, R)(auto ref R i) {
>>>         return cast(S)i*2;
>>>     }
>>>
>>> and you should get further.
>>
>> But surely nested template should be able to access outer 
>> template's
>> parameter.
>
> If you have to instantiate it to see how to instantiate it, it 
> doesn't work. General rule of thumb on templates. IFTI only 
> works at one level.
>
> -Steve

I can't see any IFTI in my code, can you point it out?